The opening of available television (TV) Band spectrum for usage by secondary TV band devices has created a need for efficient spectrum sensing mechanisms that can reliably detect available TV band white spaces to ensure that primary TV band users such as DTV broadcasters and wireless microphones are protected from interfering broadcasts by secondary TV Band device users.
Sensing for available white spaces in the VHF/UHF bands is vital to the operation of secondary TV Band devices. Protection of primary incumbent operators like digital television (DTV) stations and wireless microphone operators is designated by the United States Federal Communications Commission (FCC) and other federal authorities around the world. The DTV and wireless microphone sensing requirements set forth by the FCC are very stringent, requiring a sensing receiver sensitivity of −114 dBm for DTV and −107 dBm for wireless microphones. Detecting primary user broadcasts on VHF/UHF channels at the required sensing sensitivities is very challenging.
It has been suggested that all primary users of the TV Band spectrum broadcast a pilot tone at the DTV pilot position. Current methods of DTV pilot tone sensing rely on an accurate knowledge of received noise power. A signal energy contained within a narrow frequency band centered at the anticipated pilot tone position is compared against a threshold that is based on knowledge of, or an estimate of, the noise present in the channel. This technique is vulnerable to inaccuracies in the estimation of the noise, which often causes substantial degradation in performance. Furthermore, the presence of unwanted interfering tones within the DTV signal bandwidth can seriously affect DTV pilot tone detection performance.
There therefore exists a need for a method and apparatus that can detect the presence of DTV pilot tones at very low received signal strengths and in the presence of interference.